1. Field of the Invention
The present invention relates to high pressure gas containment devices, and in particular, natural gas and hydrogen gas storage vessels composed of concentric shells having reduced weight and at reduced cost.
2. Description of the Prior Art
The use of alternative fuels such as natural gas and hydrogen is expanding rapidly worldwide, as the growing automotive industry is seeking sustainable, ecologically cleaner, and less expensive fuels.
Natural gas and hydrogen fuel are commonly stored in pressure vessels on-board vehicles, highly compressed to improve the gravimetric energy density and volumetric storage efficiency of these gaseous fuels. Compressed gas vessels must be strong and resistant to cyclic loading, corrosive chemicals, temperature extremes, abrasion and impact loads, as well as resistant to the corrosive constituents of natural gas or hydrogen fuel.
At present, on-board fuel storage vessels can be divided into the following three types of cylindrical pressure vessels, depending on the materials used in their manufacture:    1) All-Metal: for example, 4130 steel alloy or 6061 aluminum alloy,    2) Metal-Composite: for example, 4130 alloy steel or 6061 aluminum alloy liner with carbon/glass/aramid fiber-reinforced composite overwrap, and    3) All-Composite: for example, carbon/glass/aramid fiber-reinforced composite overwrap on a thin plastic film liner.Each of the three types of high pressure vessels is widely available in the market, and has its own set of advantages and disadvantages.
All-metal vessels are most common due to their low-cost and economies of scope with the ubiquitous industrial gas vessels. However, the heavy weight of metal vessels is a serious disadvantage in automotive on-board fuel storage applications as weight impacts vehicle fuel efficiency, payload or passenger capacity and operational characteristics.
Metal-composite vessels are built to be lighter than all-metal vessels by partially replacing metal with a lower-weight carbon, glass or aramid fiber composite overwrap. However, carbon and aramid fiber composites are very expensive compared to metals. While glass fiber is less expensive compared to carbon fiber, this material suffers from weak corrosion resistance and limited durability under high stress conditions.
All-composite vessels are significantly lighter than all-metal or metal-composite vessels by fully replacing metal with a lower-weight carbon, glass or aramid fiber composite shell, as well as replacing the metal liner with a plastic liner.
High pressure on-board fuel storage vessels—either natural gas or hydrogen cylinders—are currently required to be designed for 15-year service life, comprising up to 15,000 pressurization-depressurization cycles, while also subjected to internal and external corrosive elements, temperature extremes and mechanical damage from abrasions and impact. Such requirements restrict material choices to a limited range of metal alloys such as 4130 steel and 6061 aluminum alloys and advanced fiber-reinforced composites.
Therefore, there still remains a need for on-board fuel storage vessels that have a reduced weight compared to traditional all-metal vessels, and which have a reduced cost when compared to composite alternatives.